OpenRPC Support

[stephenberry]

Add OpenRPC specification support for the registry

Adds the ability to generate OpenRPC 1.3.2 specification documents from a glz::registry, enabling machine-readable API discovery for REPE and JSON-RPC services.

New API

• registry::open_rpc_info — set API title, version, and description
• registry::open_rpc_spec() — generate the full glz::open_rpc document
• registry::register_open_rpc() — register a /open_rpc endpoint that serves the spec (works with both REPE and JSON-RPC protocols)

All registered endpoints (variables, functions, member functions, objects, root) are included as methods with JSON Schema descriptions for their parameters and return types, generated via the existing write_json_schema infrastructure.

Bug fix: to_json_schema stack overflow on function pointers

The to_json_schema nullable specialization in schema.hpp used the nullable_t concept, which matches raw function pointers (bool(t) and *t both work). Dereferencing a function pointer yields a function reference, std::decay converts it back to a function pointer, causing infinite template recursion. Fixed by using the existing nullable_like concept which already excludes function pointers via !is_function_ptr_or_ref<T>.

Files changed

• include/glaze/rpc/openrpc.hpp (new) — open_rpc, openrpc_info, openrpc_method, openrpc_content_descriptor, method_metadata structs
• include/glaze/rpc/registry.hpp — metadata capture during on(), open_rpc_spec(), register_open_rpc()
• include/glaze/json/schema.hpp — nullable_t → nullable_like in to_json_schema specialization
• docs/rpc/openrpc.md (new) — documentation
• mkdocs.yml — added OpenRPC to nav
• tests/networking_tests/openrpc_test/ (new) — 8 test cases, 59 assertions